Each Front End Server runs the following components involved in conferencing:
- Focus Factory
- Conferencing Servers (MCUs)
- Conferencing Server Factory
- Internet Information Services (IIS)
- Other Front End Server components
The Focus is the conference state server. It is implemented as a SIP user agent that is addressable by using a conference URI. The Focus runs in the User Services module of all Front End Servers. All group IM, multiparty A/V, and data collaboration sessions are managed on the server by the Focus.
The Focus is responsible for the following tasks:
- Initiating conferences
- Enlisting required conferencing servers
- Authenticating participants before allowing them to enter a
- Enforcing the policy that specifies whether the meeting
organizer is authorized to invite external users
- Maintaining SIP signaling relationships between conference
participants and conferencing servers
- Managing conference state
- Accepting subscriptions to conferences and notifying users of
changes in conference state, such as the arrival and departure of
participants and the addition or removal of media
- Maintaining and enforcing conference policies and rosters
The Focus also enables the presenter to lock a meeting so that no more participants can enter.
A separate instance of the Focus exists for each active conference.
The Focus Factory is responsible solely for scheduling meetings. When a user creates a new meeting, the meeting client sends a SIP SERVICE message to the Focus Factory, which creates a new instance of the meeting in the conference database and returns information about the newly created meeting to the client.
Conferencing Servers (MCUs)
Supporting multiparty conferences requires a server known as a conferencing server (also known as an MCU or multipoint control unit). A conferencing server is a pluggable component that is responsible for managing one or more media types. Office Communications Server 2007 R2 includes five conferencing servers:
IM Conferencing Server.Enables group IM by relaying IM
traffic among all participants. When a third participant is added
to a two-party IM conversation, the initiating client invites the
IM Conferencing Server to the conversation. From that point, all
messages among the participants are routed through the IM
Telephony Conferencing Server.
Manages audio conferencing provider (ACP) integration.
Supports both dial-out and dial-in, as well as standard third-party
call control features such as mute and eject. The Telephony
Conferencing Server does not support mixing VoIP and PSTN in the
same call. To connect dial-out to PSTN endpoints, a Mediation
Server is required; for details, see
Office Communications Server 2007 R2 adds a new Dial-in Conferencing feature, which provides an on-premises audio bridge that external users can use to dial in to the conference with PSTN devices. For details, see New Dial-in Conferencing Featurein New Server Features in the Getting Started documentation and Dial-in Conferencing Architecture.
Web Conferencing Server.Manages conference data
collaboration, including native support for Microsoft Office
PowerPoint presentations, Microsoft Office document sharing, white
boarding, application sharing, polling, Q&A, compliance
logging, annotations, meeting summaries, handouts, and various
multimedia formats. The Web Conferencing Server uses Persistent
Shared Object Model (PSOM), a Microsoft Office Live Meeting
protocol, for uploading slides to a meeting.
A/V Conferencing Server.Provides multiparty IP audio and
video mixing and relaying, including the Microsoft RoundTable
conferencing device, by using Secure Real-time Transport Protocol
(SRTP) and Secure Real-time Transport Control Protocol (SRTCP).
Application Sharing Server.New for Office Communications
Server 2007 R2, this conferencing server enables the Desktop
Sharing feature, which enables users to transmit a view of their
desktop to others during a conference. For details about this
Sharing Featurein New Server Features in the Getting Started
Conferencing Server Factory
When the Focus requests a particular conferencing server for a meeting, the Focus sends the request to Conferencing Server Factory, which determines which conferencing server is available to service the request and returns its URL to the Focus. The Conferencing Server Factory is responsible for provisioning a meeting for a particular media type on a Conferencing Server by using the local policies for creating meetings. A Conferencing Server Factory provisions meetings according to local policies and takes into account the current load on the Conferencing Servers before assigning one to a meeting.
Internet Information Services (IIS)
Office Communications Server requires the IIS component to be installed on every Front End Server. Office Communications Server relies on IIS for the following functions:
- The Live Meeting client uses IIS to download meeting content
(such as PowerPoint presentations).
- Office Communicator uses IIS to download Address Book Server
- Address Book Web Query service uses IIS to enable Microsoft
Office Communicator Mobile for Windows Mobile clients to query for
global address list information without downloading Address Book
- Device Update Service uses IIS to provide updated versions of
client software, such as Microsoft Office Communicator and Office
Communicator Phone Edition, to users.
- An ASP.NET application running on top of IIS is used for the
Group Expansion Web Service, which enables Office Communicator to
expand distribution groups for purposes of group IM.
Other Front End Server Components
Other important Front End Server components include the following:
SIP Proxy.The SIP Proxy (also known as the protocol stack or
SIP stack) is the core protocol platform on which all other
services are built. It provides the basic structure for networking
and security and performs connection management, message header
parsing, routing, authentication, and state management.
HTTP.SYS.The IIS kernel-mode HTTP protocol stack. HTTP.SYS
queues and parses incoming HTTP requests and caches and returns
application and site content.
User Services.Provides closely integrated IM, presence, and
conferencing features built on top of the SIP Proxy. It also
includes the Focus and Focus Factory.
User Replicator.Updates the user database to be synchronized
with Active Directory Domain Services (AD DS). The Address
Book Server uses information provided by User Replicator to update
information from the global address list.
Server API.Provides basic scripting capability for creating
custom message filters and routing applications. The scripts can
either run in process or, where required, can be dispatched to a
managed code application that is running in a separate process.
RTC Aggregate Application.Handles the aggregation of
presence information across multiple endpoints.
Address Book Server.Provides global address list information
from Active Directory Domain Services to Office Communicator
clients. It also retrieves user and contact information from the
RTC database, writes the information to the Address Book files, and
then stores the files on a shared folder where they are downloaded
by Office Communicator clients. The Address Book Server writes the
information to the RTCAb database, which is used by the Address
Book Web Query service to respond to user search queries from the
2007 R2 version of Office Communicator Mobile. It optionally
normalizes enterprise user phone numbers that are written to the
RTC database for the purpose of provisioning user contacts in
Office Communicator. The Address Book Server is installed by
default on all Front End Servers. The Address Book Web Query
service is installed by default on all Web Components Servers.
Intelligent IM Filter.Filters incoming IM traffic by using
administrator-specified criteria. It is used to block unsolicited
or potentially harmful IM items from unknown endpoints outside the
VoIP Components.For details about Front End Server
components used for VoIP, see
Archiving Agent.Captures IM for archiving and sends it to a
destination queue on an Archiving Server.
CDR Agent.Intercepts SIP messages and uses them to send Call
Detail Record (CDR) data to a destination queue on a Monitoring
QoE Agent.Receives SIP service messages that report call
quality metrics and sends them to a destination queue on a